In the processing of fabrics, particularly knitted fabrics, and more particularly still tubular knitted fabrics, preliminary processing operations typically include one or more wet processing operations such as washing, bleaching, dyeing, etc. In connection with at least some of these operations, the wet processed fabric is deposited in "rope" form into a container, to await further processing, frequently at a different location in the plant.
Further processing of the wet, rope-form fabric may involve preliminary steps of lifting the rope-form fabric out of its container and directing the fabric onto the entry section of a spreading device, for example. In the case of tubular knitted fabric, the spreading device typically is received internally of the fabric tube and serves to spread the fabric out to a flat, two-layer form, accompanied by lateral distention of the fabric to a desired width.
Typically, as wet processed fabric is lifted from its container, it may be severely twisted such that, as the fabric rope approaches the entry end of a spreader, the spreader may be unable to open up the fabric to allow the fabric to pass over the spreader frame. Were such a condition to occur, it would at best require immediate shut-down of the processing line while the condition was corrected. At worst, it could result in damage to both the spreader and to the fabric.
It has been common practice, in the past, to deal with the twisted fabric condition by placing the fabric container on a turntable, directly below a lifting roller by which the fabric is withdrawn from the container. A twist sensing device, in itself well known, is associated with the rope-form fabric at a point adjacent to the lifting roll, typically on the discharge side thereof. When the sensing device detects a twist condition in the fabric, a drive motor for the turntable is actuated to rotate the turntable in a direction tending to correct that condition.
Because the lifting roll frequently is spaced well above the supply of fabric in the container, a considerable response time can be involved between initiating rotation of the turntable (and the fabric container supported thereon) and the sensing of the effects thereof by the twist sensor. This arrangement can lead to a great deal of over-rotation or "hunting" of the turntable and fabric container. In the prior art, this problem has been dealt with by providing a second, upper level detwisting device, arranged to operate in synchronism with the corrective rotations of the turntable below, but acting directly upon the rope-form fabric itself at a point closely adjacent to the lifting roller. This arrangement provides for a rapid corrective response to the sensing of a twist condition, and avoids the excessive over-rotations of the turntable which were observed with more primitive systems. An example of the use of such an upper level detwisting device is disclosed in the Zerle et al. U.S. Pat. No. 4,329,838.
The present invention is directed to a novel and improved, simplified and more economical form of upper level detwisting mechanism for the purposes described. To this end, the detwisting mechanism of the invention is compact and lightweight, very economical to manufacture, yet ruggedly constructed and altogether suitable for the purpose intended. The mechanism of the invention includes a rotatably supported annular member through which the fabric rope passes in travelling from the supply container to the lifting roller. The annular member carries a pair of resiliently biased, opposed rollers that grip the fabric as it passes through. A reversible drive motor is mounted adjacent the annular member and is connected thereto by elastic belt means. The reversible drive motor is controlled in parallel with the rotational drive of the turntable below, so that the annular member is rotated in synchronism with the turntable. The fabric, which is gripped between the resiliently biased rollers, is rotated directly by such rollers, in accordance with rotations of the annular member, as controllably rotated by the drive motor.
In a specifically preferred embodiment of the invention, the annular member referred to above is a substantially conventional poteye, which is a commonly employed guiding element frequently used in the textile industry and widely available at low cost and in various sizes. The poteye is a ring-shaped element whose walls are of radially outwardly opening U-shaped cross section, defining upper and lower flanges and an intermediate annular recess. In the detwisting mechanism of the invention, such a poteye is mounted for rotation about a vertical axis by three or more annularly grooved support rollers which engage the lower flange of the poteye at spaced points about its periphery. The upper flange of the poteye serves to mount resiliently biased pivot arms, carrying gripping rollers at their upper ends. The annular recess formed between the upper and lower flanges serves to receive elastic driving belts, for controllably rotating the poteye. The arrangement is unusually simple and economical, yet rugged and reliable.
In another preferred form of the invention, a safety shut-off device is incorporated with the upper level detwisting mechanism whereby, if a tangled or knotted portion of the fabric rope approaches the detwisting mechanism, it is sensed in advance and the operation of the lifting roller is immediately halted, to prevent damage to the detwisting mechanism and/or to the fabric. Advantageously, the safety shut-off device includes a second annular member, of smaller diameter than the annular member previously referred to, through which the fabric rope passes immediately before entering the detwisting mechanism. The second annular member, which most advantageously is a conventional poteye of suitable diameter, is mounted for limited vertical movement and is associated with a shut-off switch. Whenever a knot or tangle encounters the second annular member, and is unable to freely pass through it, that member will be lifted by the upwardly moving fabric rope, causing the mechanism to be immediately shut off until the problem is corrected.